US 20050217853 A1
Openings are created between a wellbore and a formation by firing a perforating gun adjacent a perforating zone in the formation and debris is removed. A tubing string extending to the formation is pressurized to a first pressure to actuate the perforating gun. A second higher pressure is applied to activate a downhole injection port. Substantially immediately thereafter fluids are injected into the wellbore near the openings and circulated to the surface for the removal of debris. An optional and uphole injection port can be used to adjust the hydrostatic head above the perforating gun with the removal or addition of fluid. The tubing string extends sufficiently above the wellbore at surface to enable lowering of the downhole injection port below the openings during fluid circulation for enhanced removal of debris.
1. A process for creating openings between a wellbore and a formation comprising:
running-in a tubing string into the wellbore to position a perforating gun adjacent a perforating zone;
pressurizing the tubing string to a first pressure to actuate the perforating gun and produce openings between the wellbore and the formation;
pressurizing the tubing string to a second pressure to actuate a downhole injection port adjacent the perforating gun; and
circulating fluid at a rate through the downhole injection port for conveying debris up the wellbore.
2. The process of
opening an uphole injection port located on the tubing string uphole of the downhole injection port; and
adjusting the hydrostatic head above the perforating gun.
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11. An apparatus for creating openings through casing between a wellbore and a formation comprising:
a tubing string extending downhole in the casing to the formation and forming an annulus therebetween;
a perforating gun at the downhole end of the tubing string and actuable at a first pressure; and
a downhole injection port located on the tubing string adjacent the perforating gun and being pressure-actuable at a second pressure, so that
when the tubing is pressurized to the first pressure the perforating gun is actuated for forming openings in the casing, and
when the tubing is pressurized to the second pressure the downhole injection port is opened to enable circulation fluid from the tubing and up the annulus so as to continuously remove perforation debris from the wellbore.
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This invention relates to a method and apparatus to perforate or re-perforate a well and then to substantially and immediately thereafter circulate a fluid for removal of solids and debris from an underground formation for an aggressive completion or stimulation.
To recover hydrocarbons such as oil and natural gas from subterranean formations through a wellbore penetrating the earth to the hydrocarbon-bearing formation, it is common to perform a completion, including perforating, and in some circumstances to perform some type of stimulation procedure in order to enhance the recovery of the valuable hydrocarbons.
In order to recover the hydrocarbons, a well is drilled from the surface to the formation. Following drilling, the well is generally completed by installing a tubular well casing in the open borehole and cementing the casing in place. Because the casing and cement forms a continuous hollow column, no wellbore fluids are able to enter the well to be transported to and recovered at the surface.
For this reason, it is common to provide openings through the casing and cement annulus in the zone of interest by perforating the casing and cement into the surrounding formation to provide access from the formation into the wellbore for recovery of the formation fluids. In situations where existing perforations are deemed inadequate the formation can be stimulated using a variety of other techniques such as acidizing, fracturing, flushing, or re-perforating, any of which can produce debris.
Forms of debris include drilling or perforation debris, debris from cementing operations, and/or mud solids. Naturally occurring debris such as sand, silts or clays can also be present. In some formations shales and shale chunks, pyrite, coal and other fragmented sections of formations can be produced. This debris should be quickly removed from the wellbore or formation in order to prevent it from causing a blockage, or eroding or damaging production equipment. In some instances the removal of increased volume of debris can substantially enhance production.
Completion or stimulation methods include a method described in U.S. Pat. No. Re. 34,451 to Donovan et al wherein a perforating gun with an external auger is mounted to a tubing string to both aid in clean-up of the debris from the perforations as well as to facilitate the movement of the gun out of the debris. The auger flights create a tortuous path increasing the velocity of produced formation fluids and improves the ability of those fluids to carry debris. Hydrostatic kill fluid is circulated to remove debris and produced hydrocarbons. Thereafter, proppent is pumped down tubing and into the formation. The auger facilitates the removal of the gun packed in the sand.
In U.S. Pat. No. 4,560,000 to Upchurch a well perforating technique actuates a firing mechanism of a tubing-conveyed perforating gun using a pressure difference between at different points in the borehole. The technique obtains the benefit of underbalanced conditions to aid in creating a localized cleansing effect as the formation fluids enter the well casing.
Further, Applicant was part of the development of an aggressive perforating-while-foaming (PWF) production process to increase the production capability of a well. This process has gained wide usage over the last 4 years within the heavy oil industry, specifically wells drilled into unconsolidated sandstone formations. This method produced more sand in a shorter period of time than other more traditional methods. It is strongly suspected that this immediate removal of sand is linked to the superior performance of these wells. A perforating gun is tubing conveyed down an underbalanced well. The gun is detonated using a drop bar and remote trigger. Foam is almost simultaneously injected and continuously circulated through the wellbore, carrying with it debris from the formation.
Although continuous circulation of foam effectively removes debris from the wellbore in the PWF process, the remote trigger can create un-safe work practices as a result. As well, drop-bars are not considered practical in highly deviated wells since the bar may not reach the bottom. Upchurch relies solely on formation pressure to clean out the wellbore, which can be insufficient in low pressurized formations and can prevent comprehensive elimination of debris from the wellbore. Donovan's method is also dependent on formation pressure to clean out the perforation debris from the wellbore, but is aided by the auger blades. Removal of wellbore debris is not a controlled factor in either case. If debris is not completely removed from the wellbore, it may block perforations, limit production, damage production equipment, or plug the outside or the inside of the production tubing reducing, partially or totally restricting production. In such instances, well clean-out procedures would be repeatedly required at a large expense.
A process is described for creating openings in a well casing and which substantially and immediately accommodates clean-up and production of debris. In a preferred embodiment, a pressure-actuated perforating gun is fired adjacent a zone in the formation to be perforated for forming openings. Substantially immediately thereafter, a fluid is continuously injected through a downhole pressure-actuated injection means or port near the openings and is circulated up through a wellbore at a sufficient velocity or elutriation rate overcome settling of debris and therefore to remove and lift debris from the formation. Optionally, an uphole foam injection means or port can aid in adjusting the hydrostatic head above the perforating gun. The tubing string extends sufficiently above the wellbore at surface to enable lowering of the tubing string and downhole injection means or port to below the openings for enhanced removal of debris.
In a broad aspect, a process for creating openings between a wellbore and a formation comprises running-in a tubing string into the wellbore to position a perforating gun adjacent a perforating zone, pressurizing to a first pressure to fire the perforating gun and produce openings between the wellbore and the formation, pressurizing to a second pressure to actuate a downhole injection means and injecting fluid therethrough at a sufficient velocity or elutriation rate to convey debris from the wellbore by circulating the fluid out through the downhole injection means of the wellbore to at surface. It is preferable to lower the tubing string during circulation so as to re-position the location of the downhole injection means to below the openings. Typically thereafter the tubing string is then removed.
In another broad aspect, an apparatus for creating openings between a wellbore and a formation comprises a tubing string in the casing and extending downhole from surface for positioning a perforating gun adjacent a perforating zone and forming an annulus between the tubing string and the casing, a downhole injection port located on the tubing string for injection of fluid at an elutriation rate so as to continuously remove debris from the wellbore, and means to pressurize the tubing for firing the perforating gun and opening the downhole injection means. An uphole foam injection means can be located on the tubing string for cleaning out the well and displacing wellbore fluid to create a desired fluid level.
With reference to
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Fluids 24 are chosen for their elutriation characteristics, such as density, viscosity, and flow velocities as well as how they interact with wellbore fluid 46 and formation fluids 66. The possibility of formation damage should always be considered when choosing a fluid 24. Fluid 24 options can include low density foams, gases, or liquids.
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With reference also to
The apparatus enables injection of fluid 24 for lifting debris from the wellbore 16 such as when there is not sufficient formation production volume or pressure to remove the debris or where the debris has a high enough density to be unaffected by usual formation production. Circulation of a suitable fluid 24 can be implemented providing enhanced lift. Such fluid 24 is circulated at sufficient velocity, viscosity and density or elutriation conditions and rates to remove the debris.
Generally, a fluid level 62 is established above the perforating gun 22. Circulation of fluid 24 is established through the fluid injection inlet 38 at the surface 26 and wellbore fluid 46 and fluid 24 are recovered through the spool 28 at the surface 26. Additionally, the downhole injection port 42 is preferably a conventional pressure-activated ‘S’ drain or burst plug 50.
As shown in
The tubing string 40 is pressurized
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Circulation of the fluid 24 conveys or aides the conveyance of the debris up the wellbore 16 to the surface 26 for removal of substantially all debris.
Once the operation is complete and sufficient debris has been removed from the wellbore 16, the well's productivity thereafter is increased.
In an alternate embodiment, and returning at
In another embodiment of the invention, at
The preferred fluid 24 is low density foam. Inherently, foam has a high viscosity at low shear rates making it extremely useful as a circulating medium in low pressure reservoirs. These properties minimize fluid loss to the formation and reduce needed annular velocities yet provide sufficient debris elutriation with high lifting capability at minimum circulating pressures. Circulation conditions including foam generated with natural gas or nitrogen instead of air can be used to clean out higher pressure wells.
Alternatively, production fluids can also be used. A variety of natural and process additives or polymers are available to increase the lifting, carrying and suspending capability of the fluid.
It will be readily apparent to those skilled in the art that many variations, application, modifications and extensions of the basic principles involved in the disclosed embodiments may be made without departing from its spirit or scope.
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